Medical image viewing tools typically include features for delineating “regions of interest” (ROIs). An ROI is normally graphically indicated with a line outlining the shape of the region; sometimes a geometric shape such as an ellipse or rectangle, sometimes a hand drawn or algorithmically defined irregular shape. The line is known as a boundary. A boundary has no thickness or width, yet to visually depict or represent a boundary or a line, the boundary or line is visually depicted having a thickness or a width. By necessity, the thickness or width of the line overlays some part of the image. While various standards exist for the relationship between image data pixels and mathematical ROI boundaries, there is no agreed upon standard of how finite with graphical outlines map to the mathematical boundaries. Drawing the center line of the graphical object at the mathematical boundary is a common implementation, but other implementations place the mathematical boundary at the inside edge of the graphical outline.
When there is a need to indicate very precisely where the interior/exterior boundary, lies the thickness of the line used to mark the outline gives rise to ambiguity. A question arises as to whether the region boundary is located at the inside, middle, or outside of the line. Thus, visually depicting a boundary of a ROI using a line having a thickness or a width is inadequate.